The present invention generally relates to engine control systems for automotive vehicles and, more particularly, to a method of controlling engine stability based on a fuel modifier.
2. Discussion
Recent advances in automotive vehicle engine control systems have led to the development of dynamic crankshaft fueling control systems. For instance, commonly assigned U.S. Pat. No. 5,809,969, entitled "Method for Processing Crankshaft Speed Fluctuations for Control Applications" issued Sep. 22, 1998, which is hereby expressly incorporated by reference herein, discloses one such dynamic fueling control system. According to this system, the amount of fuel delivered to the engine is reduced to obtain superior catalyst light off and engine out hydrocarbon reduction. However, as the fuel to air ratio is leaned out, the engine's burn rate is slowed down and engine stability becomes rougher. Such engine roughness is quantified in the art as the coefficient of variance of torque or COV. Thus, with the reduction of fuel, overall drivability of the vehicle becomes harder. From a calibration stand-point, this trend is particularly noticeable when 1300 drivability index fuel is used.
In view of the foregoing, it would be desirable to provide a system for use in conjunction with a dynamic crankshaft fuel control system to reduce COV and engine roughness.